CANWARN is an organization of volunteers, boots-on-the-ground, who report severe weather to Environment Canada - some of these volunteers are also Amateur Radio Operators. When Environment Canada's weather centres issue severe weather watches or warnings, they may alert CANWARN volunteers at the organization's regional stations in the affected areas. Those volunteers who are also Amateur Radio Operators can contact other CANWARN members via amateur radio, advise them that a watch or warning has been issued, and ask them to report signs of approaching severe weather. These signs can include intense lightning, hail, cumulonimbus clouds (CBs), and funnel clouds.

CANWARN is organised in local networks. When CANWARN members spot severe weather, they send their reports to the CANWARN net controller who then forwards them to Environment Canada's severe weather office in Toronto using either a special telephone number or e-mail address. At the weather office, the severe weather meteorologist combines the data from the satellites and radar with the information from the ground to refine the forecast or prepare a severe weather watch or warning. CANWARN stations can be equipped with computers, printers, and ham radio equipment, and can be located in community centres such as airports, police stations and senior citizens complexes.

Sudbury CANWARN:There are numerous Environment Canada trained weather spotters in the Greater Sudbury area. Those who are amateur radio operators can start up an official CANWARN severe weather Net on one of the local repeaters when there is a severe weather watch/warning issued and there is severe weather detected or approaching the area.